Consumers use paper wiping products, such as tissues, for a wide variety of applications. For example, various types of tissues can be used for applications, such as for nose care, cosmetics, eyeglass cleaning, etc. Typically, a user of such tissues requires that the tissues possess a relatively soft feel. Moreover, a user often desires that the tissue be capable of absorbing a certain amount of a liquid without substantially wetting the user""s hand during use. In the past, various mechanisms have been utilized to produce tissues having a soft feel. For example, in many cases, a tissue is softened through the application of a chemical additive (i.e., softener) that is capable of enhancing the soft feel of the tissue product. Moreover, in other instances, a side of the tissue is imparted with domes to provide a softer feel.
In the past, domes were typically imparted onto a tissue surface by the application of pressure. For instance, one prior art tissue forming process is described in U.S. Pat. No. 5,556,509 to Trokhan, et al., which is incorporated herein in its entirety by reference thereto. Trokhan describes a process for forming a web by adhering the web to a surface of a heated dryer drum and pressing it between the drum and a roller at a nip to form a web surface with different elevations. Thereafter, the web is creped from the dryer and wound up at a reel. However, one problem with such conventional tissues is that they typically have a xe2x80x9ctwo-sidedxe2x80x9d feel. Moreover, such conventional tissues also generally have relatively poor absorption properties. For example, a conventional tissue, such as described above, is generally characterized as having relatively high density regions and relatively low density regions. (See e.g., Trokhan). Accordingly, these conventional tissues possess a substantial fiber density gradient in the x-y plane (or the plane formed by the machine direction and cross-machine direction), while possessing a relatively low fiber density gradient in the xe2x88x92z direction so that a higher fiber density gradient exists in the x-y plane than in the xe2x88x92z direction.
As a result of such density gradients, the conventional tissues discussed above also have a substantial pore size distribution gradient in the x-y plane and a relatively low pore size distribution gradient in the xe2x88x92z direction so that a higher pore size distribution gradient exists in the x-y plane than in the xe2x88x92z direction. For example, a conventional tissue has larger pores formed by the low density regions and smaller pores formed by the high density regions. However, because liquids normally flow at a faster rate through larger pores than smaller pores, a user""s hand can be easily wetted when using the prior art tissue. Specifically, water can flow readily flow through the pores of the low density regions onto a user""s hand.
As such, a need currently exists for an improved process for forming a tissue that possess a soft feel and good absorption properties.
The present invention is generally directed to a process for forming a tissue with surfaces having elevated regions. In particular, a process of the present invention can impart one surface with one topography and the other surface with a different topography. In general, the present invention is directed to a method for forming xe2x80x9celevated regionsxe2x80x9d onto a surface of a tissue. As used herein, xe2x80x9celevated regionsxe2x80x9d generally refer to any type of shape imparted onto a tissue surface including, but not limited to, dome, parabola, hyperbola, inverted cone, multiples or combinations thereof or variable contour shapes. In particular, a tissue made in accordance with the present invention can be provided with two surfaces having elevated regions so that the surfaces have at least one different topographical characteristic, such as a different pitch depth, number (i.e., number of elevated regions in a given area), pitch width, direction, etc.
To form elevated regions onto each tissue surface, a variety of well-known papermaking techniques and devices can be utilized. In particular, devices containing protrusions, such as patterned fabrics, patterned rolls, wire-mesh, etc., can be provided to form elevated regions on the surface of a tissue when contacted therewith. Moreover, various papermaking techniques, such as through-air drying, creping, embossing, calendering, etc., can be utilized when forming the tissue.
In one particular embodiment, for example, the tissue can be formed utilizing a technique known as uncreped through-air drying. In this embodiment, a fibrous web is first deposited onto a forming fabric. From the forming fabric, the web is then transferred to a transfer fabric with the assistance of a vacuum box or shoe, if desired. During this transfer stage (i.e., xe2x80x9crush transferxe2x80x9d), the consistency of the web is typically less than about 35% dry weight, and particularly between about 15% to about 30% dry weight. In one embodiment, the transfer fabric can also be provided with protrusions, as stated above, to impart elevated regions onto one surface of the tissue. The protrusions of the transfer fabric can generally vary as desired. For example, the transfer fabric can have protrusions of a pitch depth greater than about 0.010 mm, particularly between about 0.025 to about 2 mm, and a pitch width greater than about 0.001 mm, particularly between about 0.005 to about 5 mm. In addition, the transfer fabric can also have differing protrusion directions, number per unit area, shapes, etc.
From the transfer fabric, the fibrous web is then transferred to a through-air dryer to substantially dry the web, although other dryers are equally suitable. In some embodiments, for example, the web can be transferred from the transfer fabric to the through-air dryer at a consistency less than about 60% by weight, and particularly between about 25% to about 50% dry weight.
The through-air dryer, in some instances, can also contain a device for imparting elevated regions onto a surface of the tissue. For example, the device can be a wire-mesh surface or a patterned fabric wrapped around the through-air dryer. In one embodiment, a through-drying fabric can be utilized that has certain protrusions of a pitch depth greater than about 0.010 mm, particularly between about 0.025 to about 2 mm, and a pitch width greater than about 0.001 mm, particularly between about 0.005 to about 5 mm. In addition, the through-drying fabric can also have differing protrusion directions, number per unit area, shapes, etc.
As stated, in another embodiment, the through-air dryer can contain wire-mesh that also has spaces defined by certain wire protrusions. For instance, in most embodiments, the wire-mesh is formed such that the spaces make up at least about 20% of the overall area of the total wire-mesh surface area. In one embodiment, for example, the wire-mesh surface can contain wire protrusions having a diameter of about 0.029 mm and also spaces defined by the protrusions having an area of about 0.005 mm2. In some embodiments, other devices, such as a pressure roll, can also be utilized to apply pressure to one or more surfaces of the tissue. For instance, in one embodiment, a pressure roll can press the tissue against the through-air dryer as the tissue travels through a nip. The pressure roll can have a smooth or patterned surface, or can have a smooth or patterned fabric wrapped around the roll. Moreover, in some embodiments, the pressure roll can apply a pressure less than about 60 pounds per square inch (psi), and particularly between about 35 to about 40 psi, to one or more surfaces of the tissue.
As a result of the process of the present invention, a tissue is formed with two surfaces having elevated regions. In particular, each surface is formed with elevated regions having at least one different topographical characteristic, such as, pitch depth, pitch width, number per unit area, shape, direction, etc. For instance, in some embodiments, one surface of the tissue has at least about 50% more elevated regions per square inch than the other surface of the tissue, and particularly between about 50% to about 300%. Further, the pitch depth of the elevated regions of one surface of the tissue, in some embodiments, is between about 20% to about 100% greater than the pitch depth of the elevated regions of the other surface of the tissue. Moreover, a tissue formed according to the present invention has a substantial fiber density gradient in the xe2x88x92z direction. Further, a tissue formed according to the present invention can also have a relatively low fiber density gradient in the x-y plane so that a higher density gradient exists in the xe2x88x92z direction than in the x-y plane.
By providing a tissue with such a fiber density gradient(s), the resulting tissues can have a variety of improved characteristics, such as improved absorbency. In particular, tissues formed according to the present invention can also have a substantial pore size distribution gradient in the xe2x88x92z direction and a relatively low pore size distribution gradient in the x-y plane so that a higher pore size distribution gradient exists in the xe2x88x92z direction than in the x-y plane. For instance, by having a substantial pore size distribution gradient in the xe2x88x92z direction, the tissue can absorb liquids at a slower rate. Further, as a result of having a relatively low pore size distribution density gradient in the x-y plane, the tissue can also act as a liquid transfer barrier for liquid flowing through the tissue.
Other features and aspects of the present invention are discussed in greater detail below.